fatigue life

[batter1979]

ok. Can any of you tell me what AGMA standards include. Predicting fatigue life for spiral bevel gears,and involute spline couplings.
I think they might be AGMA2003-c10 for the bevel gears , and AGMA 2101-d04 for the spline couplings ,. But am not 100% sure

 

[TVP]

AGMA 2003-C10 definitely discusses pitting and fatigue resistance of bevel gears. AGMA 2101-D04 covers involute spur and helical gears. It is not strictly a standard for splines.

 

[batter1979]

I just spoke With Amir at agma. There currently is no standard that covers fatigue life for involute splines. SAE b92.2 metric module has some tensile and compressive stress stuff, but does not cover fatigue. For as long as involutes have been used i find it very hard to believe nothing is published for fatigue life of an involute spline.

 

[gearcutter]

Fatigue life of splined couplings would be extremely difficult to predict.
It might be possible under laboratory controlled conditions with absolutely zero misalignment between the rotating members.
The calculation would require a misalignment factor which would have to change as wear increases.

Zak Gear has posted an online calculator using equations derived from an article by Darle W. Dudley “When Splines Need Stress Control”.
Surprisingly it does use fatigue and misalignment factors which are only based on constants so beware.

Here is the link:

http://www.zakgear.com/External_Spline_IN.html

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[tbuelna]

batter1979,

Depending upon the nature of how your splined coupling is used, there are different approaches to rating it for life. Most splines will be limited by contact fretting, rather than spalling or bending like a gear tooth, due to the boundary type contacts present.

With a straight involute spline operating with recirculating oil lubrication and made from HT alloy steel, a general rule of thumb is to design for a simple contact stress (P/A) of around 5ksi. With case hardened steel crowned splines, contact stresses up to 40ksi can be used. These contact stress limits are conservative, but experience has shown they will ensure unlimited life.

Hope that helps.
Terry

 

[batter1979]

Gearcutter,
That is what is in the machinists handbook, and what I am using to get shear safety factors and such. But it really doesn't take into account the endurance limit of the material. My case I am using 9310 AMS 6260. In many mechanical engineering cases. You can have a saftey factor above 1, and still the part will pre maturely fail. Especially when high contact stresses are present. The Hertzian model only does so much as well.